The accident began Process_start with failures in the non-nuclear secondary system , followed Motion by a stuck-open pilot-operated relief valve in the primary system , which allowed large amounts of nuclear reactor coolant to escape .

although the ntsb and pcu manufacturer parker hannifin had already determined Deciding that the pcu was properly working Employment , and thus not the cause of the crash , a private investigation into the crash for a civil lawsuit Legality tried by jury in a state court in los angeles , which was not allowed Preventing_or_letting to hear or consider the ntsb 's and parker hannifin 's conclusions Statement , decided Deciding that the crash was caused Causation by a defective servo valve inside the pcu , based on forensic findings from an electron microscope which determined Deciding that minute defects within the pcu had caused Causation the rudder unk and a subsequent uncontrollable flight and crash Catastrophe .

An investigation found Know that a non-return valve in the fuel system had been installed Placing the wrong way round causing Causation two of the engines to be starved Death of fuel .

the technician found Know responsible for incorrectly fitting the valve was charged under the air force act .

Following the accident , the non-return valve was re-designed so it could not be installed Placing incorrectly .

although the state of the wreckage prevented Preventing_or_letting investigators from definitively pinpointing Aiming the exact origin of the fire , an area of severe burning was found Know close to the unk fuel valve located in the cockpit between the pilot and co-pilot .

The Super Electra 's cross-feed fuel system maintained Preserving a constant pressure of approximately 4½ pounds , and there had been numerous reports of leakage in the vicinity of the valve .

Lockheed designers had not provided Supply any method by which any fuel that did leak Motion from the valve could safely be drained .

It was also difficult to maintain Preserving or inspect Scrutiny the valve due to its location .